The present invention relates to the field of hair colorants. More specifically, the invention relates to semi-permanent hair coloring systems.
There are a number of goals that are routinely considered in the development of a successful hair dye formulation, particularly semi-permanent or permanent dyes. First, the dye should provide a natural looking, durable and an even deposit of color on the hair. To achieve this, the dye must be able to penetrate the cuticle, and not wash out easily over a determined period of time. It is also preferred that the process that is used to achieve this end is not too harsh or damaging to the hair. Also, the color of the dyed hair should remain substantially reproducible between applications.
These goals are not simple to achieve. Depending factors are the class of dyes being used, the formula the dye is in, and process of the dye application. This is particularly difficult with semi-permanent dyes. These dyes usually have a lesser affinity to hair and intended to wash out over time. Nonetheless, they should be expected to remain in the hair for a certain length of time. The semi-permanent dyes do have certain advantages, however, in being able to produce color on the hair simply by cuticle diffusion and do not require the presence of harsh oxidizing agents to develop color.
The permanent dyes are as their name implies, more resistant to the fading process that is associated with semipermanent dyes. This type of hair coloring system is more complex however, because the dyeing process relies on the use of dye precursors. When on the hair, the dye precursors are converted to colored compounds that constitute the actual dyes that color the hair. The components of a permanent hair dye system are typically a primary intermediate, a coupler, and hydrogen peroxide. The oxidation of the primary intermediate, followed by coupling with the coupler molecule, typically produces chromophore. Although the color produced by this process is long-lasting and can achieve lightening of the hair due to bleaching of the hair shaft by hydrogen peroxide, it is not without its disadvantages. The chemical process of oxidation is usually harsh, and in order to achieve the result in a reasonable period of time must be carried out at a very high pH. Thus, the user of a permanent dyeing system runs the risk of damage to the treated hair. Also, since the chromophore is formed in situ, rather than preexisting, control of the consistency of a shade from one application of dye to the next is always problematic.
Thus, there continues to be a need for a relatively colorfast dye system that does not rely on the use of harsh oxidative processes to develop color on the hair. The present invention now provides such a system.
The present invention relates to a hair coloring system comprising a coloring-effective amount of a solubilized vat dye, and substantially no chemical oxidant, such as hydrogen peroxide. The coloring system can also confer color to hair in the absence of other coloring agents typically used for this purpose, for example, nitrophenols, aminophenols or phenylenediamines. The invention also provides a method for durably coloring the hair using solubilized vat dyes, in the absence of any added chemical oxidant.
The compounds known as vat dyes are well known. They have been used for thousands of years, examples being the naturally occurring indigo and tyrian purple. In modern times, dyes of this type have been made synthetically, and are widely used in the textile industry for dyeing of cloth, both natural and synthetic(see Joseph Rivlin, The Dyeing of Textile Fibers, Theory and Practice, Chapter 10, 1992, incorporated herein by reference). These dyes are aromatic compounds containing two or more carbonyl groups that are joined by conjugated double bonds. Unlike their permanent dye precursors, the vat dyes already contain their chromophore, and therefore do not require the presence of an oxidative agent to generate the chromophore on the hair.
The soluble vat dyes are actually a group of dyes by themselves. They are vat dyes already in the reduced soluble form, and have the unique feature that they will not oxidize by merely exposing them to the air. The soluble vat dyes are esters of the leuco vat dyes. In presence of the acid and at the proper temperature, the ester will hydrolyze to yield the leuco acid of the vat dye, which can then be oxidized even by air, as are regular leuco vats, to its insoluble form.
Solubilized vat dyes were originally used for textiles. This is because they offer many advantages:
1. The reduction step is eliminated and there is no need for careful control of the dye-bath during application.
2. The application is easier to follow since there are not large amounts of electrolytes in the dye-bath that may cause a fast-strike.
3. The solubilized vat dyes can be used in a significantly lowered pH and in diverse applications.
Soluble vat dyes have previously been disclosed for use in dyeing hair, but only in combination with a standard peroxidation system(U.S. Pat. No. 5,364,415). However, to the best of Applicants"" knowledge, solubilized vat dyes have never been used alone for the coloring of hair. Surprisingly, it was found that solubilized vat dyes out-perform other classes of dyes in the semi-permanent dye formula. For example, basic and direct dyes normally used in semi-permanent hair colors wash out after a few shampoos. Solubilized vat dyes, however, can last up to 45 shampoos.
In application, the solublized vat dye is easily penetrated into the hair and is then oxidized back to its insoluble form by simple exposure to the air. This oxidation thereby causes the dye to be retained by the hair and thus coloring the hair.
The solublized vat dyes of the invention can be any of the solublized vat dyes that are cosmetically acceptable. Vat dyes as well as solublized vat dyes encompass two chemical classes, namely the indigoids and the anthraquinone derivatives, with a preference for the anthraquinones because of their color fastness. Examples of useful solublized vat dyes include, but are not limited to, CI Solublized Vat Brown 5(CI 73411), CI Solublized Vat Black 1(CI 73671), CI Solublized Vat Red 1(CI 73361), CI Solublized Vat Green 2(CI 59831), CI Solublized Vat Violet 8(CI 73601), CI Solublized Vat Yellow 4(CI 59101), CI Solublized Vat Brown 1(CI 70801), CI Solublized Vat Red 3. The vat dyes are capable of being used alone, as the sole source of color in a dyeing composition, or in combination with another solublized vat dye. The amount of dye used is dependent upon the final shade desired, and is not particularly critical. However, the dyes are ordinarily used in an amount of about 0.5 to about 10% by weight of the composition, and preferably in a range of about 1 to about 5%.
It was discovered that the dye solution penetrates the hair very quickly, sometimes in a matter of seconds, and the color change on the hair can be observed almost immediately. Oxidation of the dyes back to their insoluble, colored, form is achieved in the absence of harsh oxidizing agents, such as hydrogen peroxide. Instead, sufficient oxidation can occur simply by exposure to air; ordinarily, however, it will be desirable to assist the dyeing procedure by exposing the hair to a hair dryer, preferably a blow dryer on a warm setting, for about 10 minutes.
Although the dyeing composition and application may indeed be as simple as described above, ordinarily the composition and methodology will employ additional features to optimize the process and produce an improved color intensity and/or color fastness. For example, a useful additive to the dye solution is one or more antioxidants. The presence of the antioxidant(s) in the formulation aids in solublization of the dye, reducing precipitation of the dye, and ensuring that the dye is in optimum form for penetration and dyeing of the hair. Examples of useful antioxidants are erythorbic acid, sodium sulfite, sodium metabisulfite, and sodium hydrosulfite. When used, the antioxidant will be present in amount of from about 0.5-5% by weight of the composition. A preferred combination is of sodium metabisulfite and erythorbic acid, particularly preferred in a ratio of about 2:1.
An additional factor that may aid in performance is the use of an alcohol in the formulation, namely benzyl alcohol. The alcohol may constitute up to about 90%, or even more, of the composition, taking into account the other necessary components of the product. However, in most cases, the amount of benzyl alcohol used will be about 0.5 to about 5% by weight.
Because the solublized vat dyes are very versatile and applicable, it is possible to combine the vat dyes with other types of semi-permanent hair dyes.
The semi-permanent dye systems of the present invention have many advantages over comparable existing dyes systems. First, the use of the solublized vat dyes avoids the use of harsh oxidants such as hydrogen peroxide, and thus reduces the possibility of hair damage due to the dyeing process so common with other dyes. The colors are also very bright, and easy to match because of its defined chromophore system. The dyes have a great affinity for the hair, and maintain an exceptional level of color-fastness even after many shampoos. The application of the dye system is also very simple, achievable in a simple rinse-off formula, with color development completed by air exposure, preferably coupled with a hair dryer at a moderate heat setting.